Chapter 2 2 Literature review

3

Chapter 2

2 Literature review

This chapter discuss about findings from the literature review. The literature review

is focused on layout planning methods, efficiency improvement in layout planning

special quality requirements in food processing industry.

2.1 Layout types

There are many definitions available for plant layout. According to Riggs, “the

overall objective of plant layout is to design a physical arrangement that most

economically meets the required output, quantity & quality” [6]. According to JL

Zundi, “plant layout ideally involves allocation of space and arrangement of

equipment in such a manner that overall operating costs are minimized” [7]. In

manufacturing systems, three main types of layouts available are product layout,

process layout, and group layout. These layouts can be further categorized into flow

line, cell, and centre. According to Tompkins [8], the distinction between these types

of layout is made based on system characteristics such as production volume and

product variety.

Figure 2-1: Layout types [8]

Pro

du

ctio

n V

olu

me

Product Variety

Product

Layout

High

Low

Low High

flow line

cell

center

Process

Layout

Group Layout

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Product layout (flow shop) is associated with high volume production and low

product variety, while process layout (job shop) is associated with low-volume

production and high product variety [8] . Figure 2-1, indicates the relationship

between production volume and product variety for various layout types.

2.1.1 Process (functional) oriented layout

In this layout similar equipment or functions grouped together, such as all lath

machines in one area and all stamping machines in another. A part worked on then

travels, according to the established sequence of operations, from area to area.

Materials can be routed through the process in any order. This type of layout is

typical for hospitals, where areas are dedicated for a particular type of medical care

[9]. Traditionally, process oriented layouts have been chosen for manufacturing of a

wide range of products in relatively small batches, and a typical production process

with a process layout is a job shop [10]. It has the advantages of flexibility, the

potential for relatively high utilisation of equipment with lower investment than

product layouts and offers high worker satisfaction. However, Evans identifies a

number of disadvantages such as high handling and transportation costs, complex

planning and control systems, low throughput times and the need for highly skilled

operators. Another problem associated with process layouts is the need for high

levels of work-in-progress (WIP) to ensure work is always available. This is because

it is difficult to pre-specify job priorities [11] .

2.1.2 Product oriented layout

A product oriented layout is defined as a set of interlinked manufacturing resources

and cells that simultaneously and in a coordinated manner address the manufacture

of a product or a range of similar products, including the necessary assembly work

[12]. In this layout, equipment or work processes are arranged according to

progressive steps by which the product is made. Production lines for shoes, chemical

plants and car washes are all product layouts [9]. Product oriented manufacturing

system may be seen as a development of traditional Cellular Manufacturing in the

sense that a set of interrelated manufacturing cells may be necessary to completely

manufacture a product, or a set of similar products, including assembly. Directing

5

systems to the manufacture of specific products can provide competitive advantages

that include short production times and improved product quality [12].

2.1.3 Cellular layout (group)

This is grouping of dissimilar machines into work cells to work on products with

similar shapes and processing requirements. A group technology layout is similar to

a process layout, in that cells are designed to perform a specific set of processes. It is

similar to a product layout, in that cells are dedicated to a limited range of products

[9]. The main reason that manufacturing companies are attracted towards

implementing cellular manufacturing (CM) layout is that the benefits of CM can

normally be realised with relatively low capital investment by relocating and

possibly duplicating certain machines as opposed to other automated strategies [13].

2.1.4 Fixed position layout

The arrangement of machines, storage areas, and/or work areas usually within the

confines of a physical structure of a manufacturing facility has significant impacts on

shop-floor productivity. Facility layout is often determined by factors such as

volume, weight of items to be produced, cost of the building to house the operation,

the product mix that must have a facility, and the fragility of the product or

component. Although not common, Fixed-Position layouts are normally used when

products are too fragile, large, bulky, or heavy to move (e.g., ships and planes). In

such configuration, machines, material, and/or workers are moved to an assembly

site (often called an assembly island) while products normally remain in one location

for its entire manufacturing (assembly) period. Advantages of fixed-position layout

include reduced movement of work items: minimized damage or cost of movement

and more continuity of the assigned work force since the item does not go from one

department to another [14].

2.2 Layout planning methods

Most of the literature of layout design falls into two major categories: algorithmic

and procedural approaches. Algorithmic approaches usually simplify both design

constraints and objectives in order to reach a surrogated objective function, the

6

solution of which can then be obtained. The majority of the existing literature is

concentrated on algorithmic approaches [15]. Procedural approaches can be

incorporated both qualitative and quantitative objectives in the design process [16]

[3].

2.2.1 Systematic layout planning

In certain type of layout problems, numerical flow of items between departments

either being impractical to obtain or does not reveal the qualitative factors that may

be crucial to the placement decision. In these situations, the venerable technique

known as systematic layout planning (SLP) can be used [9].

As the step 1 SLP begins with a data collection analysis called PQRST for the overall

production activities. It includes product (P) ‚ quantity (Q) ‚ routing (R) ‚ supporting

(S)‚ and time (T), which should be scrutinized in order to assure the validity of the

input data at the design stage. Refer Figure 2-2 for SLP procedure. In step 2 the flow

of materials analysis is carried out. All material flows from the whole production line

are aggregated into a from-to chart that represents the flow intensity among different

tool sets or departments. The step 3 "activity relationships" performs qualitative

analysis towards the closeness relationship decision among different departments. In

step 4 the relationship diagram locates departments spatially. Those departments that

have strong interactions and/or close relationships are placed in proximity. The

"space requirements" and "space available" (steps 5 and 6) determine the amount of

floor space to be allocated to each department. Space relationship diagram (step 7)

adds departmental size information into the relationship diagram of step 4.

Additional design constraints and limitations are considered before the start of block

layout generation in steps 8 to 9. In step 10, layout alternatives are developed as

design candidates. In the final step, the final design is chosen from the design

candidates [17] and the alternative layout generation is constituted [3].

7

Figure 2-2: SLP procedure [18]

The procedural approach, such as the systematic layout planning procedure has the

flexibility to incorporate a variety of design objectives, but is often lacking sound

theoretical foundation and credence to be a quality solution [16] [19].

2.2.2 Group technology

The primary activity in implementing group technology (GT) is grouping parts which

require similar processes into families and machines into cells. However, in addition

to family and cell formation, other planning and design activities have to be

performed when a facility is converted to GT. Paramount among these activities are

production planning, process planning, designing the material handling system,

determining staffing levels, and developing the layout [20]. Cellular manufacturing

(CM) and an application of GT utilises the concept of divide and conquer and

involves the grouping of machines, processes and people into cells responsible for

8

manufacturing or assembly of similar parts or products [13]. The design for cellular

manufacturing involves three stages:

(1) Grouping of parts and production equipment into cells

(2) Allocation of the machine cells to areas within the shop floor (inter-cell or

facility layout)

(3) Layout of the machines within each cell (intra-cell or machine layout) [13].

2.2.3 Graph theory

Graph theoretic approaches also handle the unequal area block plan. In these

approaches a block plan is constructed as the dual of a planar graph where nodes

represent spaces and links represent required adjacencies [21] . Developing a layout

in graph theoretic approach requires the following three steps:

(1) Developing an adjacency graph from department relationships (which

departments are adjacent)

(2) Constructing the dual graph of the adjacency graph (represent departments as

adjacent regions having specific boundaries)

(3) Converting the dual graph into a block layout (specifying departments with

regular shapes and specific areas) [22].

2.3 Other approaches

Other approaches which are also applied to facility layout problem are neural

networks, fuzzy logic and expert system [2].

2.3.1 Genetic algorithms

A genetic algorithm (GA) is a computational method modelled on biological

evolutionary process. It can be used to find a nearer-optimal solution to a problem

although there may have many near-optimal solutions in the solution terrain. The

search process is independent to the problem and the search can be performed under

many types of fitness functions [23]. Implementing the GA technique for facility

design involves five primary steps:

(1) Setting the gene structure

(2) Deciding upon the gene evaluation criteria (objective function)

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(3) Generating an initial population of genes

(4) Selecting an offspring generation mechanism

(5) Coding the process in a computer [24]

Since the modelling is done in a computer screen, various sites in the layout have to

be indicated as shown in Figure 2-3. The original site shape has to be modified to

square shapes for the coding process of computer.

Figure 2-3: Site representation [24]

To define the position of any facility on the site, a location reference is formulated by

using the column and row boundaries of the whole site. The marked cell in Figure

2-3, for example, is located in row 4 and column 4 of the grid of the whole site. The

location reference of this cell is calculated as:

Location reference = (row position - 1) X total columns + column position

Accordingly, the location reference of this cell is (4- 1) X 11 + 4 = 37. This location

reference is used to define the starting position at which a facility is to be placed on

the site.

The gene structure was set as a string of elements, each corresponding to the

location reference of a facility, as shown in Figure 2-4, and the gene length equals

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the total number of facilities. As such, each gene represents one possible solution to

the problem. To evaluate the goodness of a possible layout (a gene), an objective

function was constructed by multiplying the desired proximity weight between two

facilities by the actual distance between them, and summing for all facilities.

78 18 30 35 97 36 52 2

1 2 3 P P+1 P+2 N

61

location reference of a

fixed facility

. . . . ...

location reference of

a facility

. . . . ... . . . . ...

. . . . . . . .

P Fixed facilities N-P facilities

P = Number of fixed facilities

N = Total number of facilities

Legend:

Figure 2-4: Gene formation [24]

The objective function, as such, represents the total travel distance associated with a

given site layout. Accordingly, minimizing this objective function is required in

order to arrive at the optimum layout that results in the least travel distance.

2.3.2 Non structural fuzzy decision support systems

This is a multi objective decision aiding model. This can mainly be used for location

of construction site facility layouts. These layouts have to be changed along with the

construction process and constrains generated at that point of time. There are three

steps in using the model: Decomposition, Comparative judgement and Synthesis of

priorities. First decomposition structures a problem into elements of different levels,

each independent of those of successive levels, working downwards from goal on the

top through criteria bearing to the goal on the second level and then to sub-criteria on

the third level, and so on, working from the general (and sometimes uncertain) to the

more specific at the lower levels [25]. The merit of using a fuzzy approach is to

assign the relative importance of attributes using fuzzy numbers instead of precise

numbers [19].

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Fuzzy-based layout design algorithms modelled the fuzzy or linguistic closeness

relationship among departments. The resulting fuzzy scores that represent the desired

closeness are then used for a layout design criterion along as part of the layout

improvement process. In these methods, the fuzzy closeness determines the order of

entry of departments into the layout; but the department placement and departmental

dimensions are not explicitly considered [19]. Hence the results obtained are not very

realistic in practical implementation.

2.4 Software packages for layout planning

These are compute based algorithms designed to support the decision making

process.

2.4.1 Layout optimisation software (LayOPT)

LayOPT is a facility layout optimization software package which can be used by

layout planners and engineers to solve single and multiple floor facility layout

problems. It can be applied to manufacturing, warehouse, office and various service

facility layout problems. LayOPT allows the layout planners to generate alternative

layout plans quickly and easily and to find the optimal layout among these

alternatives. LayOPT is an improvement algorithm that starts with an existing block

layout and given the flow and cost data attempts to improve it by exchanging the

location of defined departments [26].

2.4.2 Automated layout design program (ALDEP)

The automated layout design program (ALDEP) starts by selecting the first facility

(department) at random and places it starting from a given point that represents top

left corner of the site. Then the next facility to be placed is the one that has highest

closeness relationship with the first facility. After keeping all facilities on after other,

ALDEP uses an objective function to assign a score to the layout and then repeats the

process to construct a different layout until user satisfaction is reached [24]. The

procedure used to adopt ALDEP is:

Step 1: Input following details:

Length and width of facility.

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Area of each department.

Minimum closeness preference (MCP) value.

Sweep width.

Relationship chart showing the closeness rating.

Location and size of restricted area.

Step 2: One department is selected randomly and placed in the layout.

Step 3: In this step, the algorithm uses minimum closeness required between

departments for the selection of departments to be placed with an earlier placed

department. Select the department having maximum closeness rating. If there is no

department having minimum closeness preference then any department that remains

to be placed is selected.

Step 4: If all the departments are placed in the layout, go to Step 5. Else, go to Step

3.

Step 5: Compute the total score of the layout.

Step 6: If the total score required is the acceptable score, then go to Step 7, else go to

Step 2.

Step 7: Print the current layout and the corresponding score [27].

2.4.3 Computerized relationship layout planning (CORELAP)

Computerized relationship layout planning (CORELAP) selects the first facility to be

the one with the highest closeness relationship to all others. The next facility to be

placed is the one with the highest relationship with the first selected facility. In case

of a tie, the facility with the highest relationship all other is selected, and the

procedure continues until the layout is completed [24].

2.4.4 Computer relative allocation of facilities (CRAFT)

CRAFT uses a distance based algorithm [2]. It begins with a user provided layout

and uses a more detailed method of calculating the desired closeness relationship

between facilities by considering distance, travel cost, and material flow between

facilities. It then makes a pair-wise location interchange of facilities that are either

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adjacent or have equal areas, until the layout cost cannot be reduced further [24].

CRAFT input requirements are:

1. Initial layout.

2. Flow data.

3. Cost per unit distance.

4. Total number of departments.

5. Fixed departments and their location.

6. Area of departments.

The procedures adopted in CRAFT are.

1. Determine department centroids. Final Layout

2. Calculate rectilinear distance between centroids.

3. Calculate transportation cost for the layout.

4. Consider department sharing a common border.

5. Determine transportation cost of each departmental interchange.

6. Select and implement the departmental interchange that offers the greatest

reduction in transportation cost.

7. Repeat the procedure for the new layout until no interchange is able to

reduce the transportation cost [27].

These computer algorithms focus on appropriating layout aspects like relationships

and material flow. They are not in industry use because of their limitations

(unrealistic assumptions, department shapes, consideration of building aspects like

utilities and columns, qualitative factors, etc.) [28].

2.4.5 Spiral

This is a facility layout generation and improvement algorithm. This is an adjacency

based algorithm [2]. This is a commercial software available in the market to support

the FLP. The algorithm starts with positioning departments from center point and

continues like a hologram from center to outside. The aim of any facility layout

algorithm is to better allocate the departments within facility. In order to form an

initial spiral curve, a block system is used. The width and length of the blocks are

given by user and departments are formed according to these values. Then

departments are placed around the spiral curve. The initial layout can be selected

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either randomly or with a method which is called enhanced initial layout. Enhanced

initial layout finds the highest related department and put it into center. Then adds

the other departments according to their relationships with the previous one [22].

2.5 Efficiency of a layout

A well-designed manufacturing layout plan can reduce up to 50% of the operating

cost [29] [30]. There are many key performance indicators (KPI) to analyse the

efficiency of the layout. These KPI can change with the type of the layout. Main

parameters to be considered would be:

Distance travelled (m)

Distance travelled into weight (mkg)

Goods movement

People movement

Over all equipment efficiency (OEE)

Energy efficiency

Waste minimization

2.6 Food processing technology

The primary concern of food manufacturers is to produce a product that is

wholesome, and safe, i.e. free from pathogenic micro organisms, chemical and

foreign body contamination [31]. As biological materials, foods deteriorate over time

and although this cannot be completely prevented, one aim of food processing is to

slow down the rate of deterioration by selecting appropriate methods of processing,

ingredient formulations, packaging and storage conditions [32].

Eliminating possibilities of chemical, physical and microbial contamination is a

key factor in food processing plant. The layout design should help to minimize the

direct and cross contamination. Hence the layout of the food processing factory has

to be designed to meet the safety and the efficacy of the product. This is the main

difference in the layout design of a food processing plant when compared with other

manufacturing plants. Hence common layout design methods cannot be directly

applied for food processing plants.

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2.7 Quality standards applicable for food processing

Many local and international guide lines are available in the food manufacturing

process. Based on management principles, Hazard Analysis Critical Control Point

(HACCP) and Good Manufacturing Practice (GMP) have been implemented to help

plants to maintain high levels of hygiene [4]. Quality Assurance systems (QA) can be

used to improve quality and reduce costs; HACCP programs can be used to better

assure food safety. QA and HACCP, implemented in concert, facilitate

improvements in product safety and production efficiency [33]. HACCP is widely

recognised in the food industry as an effective approach to establishing good

production, sanitation, and manufacturing practices that produce safe foods [34].

HACCP systems establish process control through identifying points in the

production process that are most critical to monitor and control [35].

A neglected area in food processing is the relation between hygiene and the

layout of the processing stages. While food hygiene has been dealt within different

disciplines and a considerable amount of knowledge is available, this knowledge is

not linked systematically to the evaluation and design of the layout in food

processing systems. The literature on layout planning has so far ignored the influence

of hygiene factors and the specific nature of food processing companies [4].